The present invention relates generally to prosthetic devices and in particular to myoelectrically controlled hook/hand systems for amputees.
In 1972, the first electrically powered hook utilizing synergetic prehension was constructed by D. S. Childress (Proceedings of the Fourth International Symposium of the External Control of Human Extremities, Dubrovnik, 1972). The electrically powered hook disclosed therein, developed by one of the present inventors, utilizes a two motor system driven by a bipolar transistor driver for selectively separating or converging two fingers which extend from a pivot. Control of the motors is effected through electrodes placed on voluntary muscles of the patient.
The use of bipolar transistors in myoelectric devices may be seen generally in U.S. Pat. Nos. 3,883,900, 3,641,993, 3,501,776, and the article "EMG Operated Electronic Artificial Leg Controller" by Saxena, published in Medical and Biological Engineering and Computer, September, 1977. However, the prior art does not reveal the use of field effect transistors in artificial limb type prosthetic devices.
In an article entitled "Artificial Hand Mechanism," published in The American Society of Mechanical Engineers in 1972, one of the present inventors disclosed the concept of synergetic prehension; wherein two motors are used for controlling an artificial hand. One of the motors is used for high-speed opening and closing of one of the pair of fingers utilized in the hand. The other motor is geared for high torque so as to apply relatively greater pinching force when the two fingers converge together for gripping of objects. Similarly, in the "Bulletin of Prosthetics Research," published Fall, 1974, one of the present inventors disclosed the concept of myopulse modulation. In myopulse modulation, the processing scheme consists of amplication of a myoelectric signal in conjunction with a small threshold. Positive and negative pulses of the myoelectric signal are amplified to saturation and an inverting stage is added to invert either the positive or negative pulses to obtain a pulse train of all positive or all negative pulses. However, a problem with this system is the relatively high quiescent electric current which requires a relatively larger size battery source.
The present invention utilizes field effect transistors to effect a significant savings of electric power. The use of field effect transistors in implanted devices, such as pacemakers, may be seen in U.S. Pat. No. 4,285,345. However, the current requirements of a pacemaker are vastly different from that of an artificial prosthetic device in which a pair of fingers must be separated by an electric motor and operated with sufficient torque to grasp an object firmly. Thus, the present design for a field effect transistor driver utilized in a myoelectrically controlled hook/hand device represents a non-obvious improvement over the prior art.